1. Field of the Invention
The present invention relates to energy transfer devices that operate on the principal of intermeshing trochoidal gear fluid displacement and more particularly to the reduction of frictional forces in such systems.
2. Background
Trochoidal gear, fluid displacement pumps and engines are well-known in the art. In general, a lobate, eccentrically-mounted, inner male rotor interacts with a mating lobate female outer rotor in a close-fitting chamber formed in a housing with a cylindrical bore and two end plates. The eccentrically mounted inner rotor gear has a set number of lobes or teeth and cooperates with a surrounding outer lobate rotor, i.e., ring gear, with one additional lobe or tooth than the inner rotor. The outer rotor gear is contained within the close fitting cylindrical enclosure.
The inner rotor is typically secured to a drive shaft and, as it rotates on the drive shaft, it advances one tooth space per revolution relative to the outer rotor. The outer rotor is rotatably retained in a housing, eccentric to the inner rotor, and meshing with the inner rotor on one side. As the inner and outer rotors turn from their meshing point, the space between the teeth of the inner and outer rotors gradually increases in size through the first one hundred eighty degrees of rotation of the inner rotor creating an expanding space. During the last half of the revolution of the inner rotor, the space between the inner and outer rotors decreases in size as the teeth mesh.
When the device is operating as a pump, fluid to be pumped is drawn from an inlet port into the expanding space as a result of the vacuum created in the space as a result of its expansion. After reaching a point of maximum volume, the space between the inner and outer rotors begins to decrease in volume. After sufficient pressure is achieved due to the decreasing volume, the decreasing space is opened to an outlet port and the fluid forced from the device. The inlet and outlet ports are isolated from each other by the housing and the inner and outer rotors.
One significant problem with such devices are efficiency losses and part wear due to friction between the various moving parts of the configuration. Such loss of efficiency can be especially severe when the device is used as an engine or motor rather than a pump.
To eliminate frictional losses, various inventors such as Lusztig (U.S. Pat. No. 3,910,732), Kilmer (U.S. Pat. No. 3,905,727) and Specht (U.S. Pat. No. 4,492,539) have used rolling element bearings. However, such bearings have been used mainly to control frictional losses between the drive shaft and the device housing rather than the internal mechanism of the device itself.
Minto et al (U.S. Pat. No. 3,750,393) uses the device as an engine (prime mover) by providing high pressure vapor to the chambers which causes their expansion and associated rotation of the inner rotor shaft. On reaching maximum expansion of the chamber, an exhaust port carries away the expanded vapor. Minto recognizes that binding between the outer radial surface of the rotating outer gear and the close-fitting cylindrical enclosure due to differences in pressure between the inner and outer faces of the outer rotor element is a problem. To obviate the effect of the unbalanced radial hydraulic forces on the outer rotor, Minto proposes the use of radial passages in one of the end plates that extend radially outward from the inlet and outlet ports to the inner cylindrical surface of the cylindrical enclosure. These radial passages then communicate with a longitudinal groove formed in the inner surface of the cylindrical enclosure.
In order to improve efficiency through friction and wear reduction when the device is used as a pump, Dominique et al (U.S. Pat. No. 4,747,744) has made modifications to the device that reduce or minimize the frictional forces. However, Dominique also realizes that one of the problems with this type of device is by-pass leakage between the inlet and outlet ports of the device. That is, the operating fluid flows directly from the input to the output ports without entering the expanding and contracting chambers of the device. To reduce bypass leakage, Dominique forces the inner and outer rotors of the device into close contact with the end plate containing the inlet and outlet ports using a number of mechanisms including springs, pressurized fluids, magnetic fields, or spherical protrusions. Unfortunately this can lead to contact of the rotors with the end plate and attendant high frictional losses and loss of efficiency. Although such losses are not a major design factor when the device is used as a pump, it is of major concern when using the device as an engine and a motor. Here such frictional losses can be a major detriment to the efficiency of the engine.
In addition to frictional losses, the basic design of the device causes wear of the gear profiles, especially at the gear lobe crowns resulting in a degradation in chamber to chamber sealing ability. For good chamber to chamber sealing, a typical gear profile clearance is of the order of 0.002 inch (0.05 mm). To provide a hydrodynamic journal bearing between the outer radial surface of the outer rotor and the inner radial surface of the containment housing, a corresponding clearance of about 0.005-0.008 inch (0.13-0.20 mm) is needed. During running, small eccentricities of the outer rotor axis cause contact of the crowns of the inner and outer rotor lobes as they pass by each other resulting in wear of the gear lobe crowns and degradation of the chamber to chamber sealing ability.
Thus it is an object of this invention to provide a trochoidal gear device of high mechanical efficiency.
It is a further object of this invention to provide a trochoidal gear device with minimum friction losses.
It is an object of this invention to provide a trochoidal gear device with minimum mechanical friction losses.
It is a further object of this invention to provide a trochoidal gear device with minimum fluidic frictional losses.
It is another object of this invention to provide a mechanically simple energy conversion device.
It is an object of this invention to set precisely the gaps between moving surfaces of the device.
It is an object of this invention to provide a low-cost energy conversion device.
It is an object of this invention to provide a direct-coupled alternator/motor device in a hermetically sealed unit.
It is yet another object of this invention to provide a device that avoids degradation of its components.
It is a further object of this invention to provide a device with an integrated condensate pump for condensed fluid cycles such as Rankine cycles.
It is an object of this invention to provide a device for handling fluids that condense on expansion or contraction.
It is an object of this invention to provide a device that eliminates wear of rotor gear profiles.
Another object of this invention is to maintain high chamber to chamber sealing ability.